Fluid catalytic cracking (FCC) is employed in petroleum refineries to convert high-boiling hydrocarbon fractions of crude oil to more valuable products like gasoline, Liquefied Petroleum Gas (LPG), and diesel. For this, heavy crude oil is chemically broken down into lighter hydrocarbon fractions having comparatively smaller chain of carbon atoms with the help of one or more catalysts. These high boiling hydrocarbons fractions are then introduced, in multiple streams, into a riser reactor section to undergo catalytic cracking. This results in lighter hydrocarbon fractions, which may be further sent to a fractional distillation column for extracting aforementioned valuable products.
As the FCC is the prime factor that governs quantity as well as quality of the final yield of any refinery, the time consumed by a FCC unit greatly influences the overall rate of production. To minimize time involved in catalytic cracking, a liquid hydrocarbon stream is vaporized inside the riser reactor to get completely diffused into the pores of the catalyst(s) used. To facilitate this vaporization process, the liquid hydrocarbon stream or the hydrocarbon feed is first atomized.
The atomization process, conducted in an atomizer, refers to the breaking down of a hydrocarbon feed of a given volume into a number of fine droplets to expand surface area or the hydrocarbon feed with respect to its own initial volume. An′ expanded surface area enhances the ease of vaporization. Also, the hydrocarbon feed is subjected to a high temperature during the atomization process which alters certain physical parameters, such as viscosity. This further enhances atomization of the hydrocarbon feed.
Conventional atomizers employed to atomize the hydrocarbon feed mix the hydrocarbon feed with steam, and the mixture so formed is routed through a nozzle orifice of the atomizer. This mixing with steam leads to division of the hydrocarbon feed into fine droplets and dispersion of these fine droplets into the steam.
However, the conventional atomizers fall short in completely and efficiently atomizing a heavy hydrocarbon feed that is extremely viscous and has a very high surface tension. Inefficient atomization leads to non-uniformity in terms of diameter and velocity of the droplets of the atomized hydrocarbon feed. Moreover, it takes considerable time for such hydrocarbon feeds to vaporize. Delayed vaporization of the hydrocarbon feed in turn leads to slow and inadequate absorption of heat by the hydrocarbon droplets inside the riser reactor, thus leading to undesirable thermal cracking and excessive production of byproducts such as coke.